The primary objective of this prospective study is to determine the relative contribution of factors that may lead to weight gain among breast cancer patients undergoing adjuvant chemotherapy in an effort to better understand its mechanistic rationale. Potential etiologic factors studied include: 1) hormones and growth factors (including total, bound, and free estradiol, androgens, SHBG, FSH, thyroid hormones, prolactin, IGF1 and II, and leptin), 2) factors affecting energy intake or expenditure including caloric intake, physical activity, and RMR, and 3) psychological factors (such as depression and quality of life). We will study approximately 140 women (including pre- and post-menopausal patients) with newly diagnosed, stage I, II, and IIIA, primary breast cancer, who will undergo adjuvant chemotherapy with currently utilized stage appropriate chemotherapeutic regimens. Body weight, body composition by dual energy X-ray absorptiometry (DXA), and the mechanistic factors described above will be measured at 3 time points, (a) baseline (prior to the first cycle or dose of adjuvant chemotherapy; (b) 2 weeks after the final administration of adjuvant chemotherapy; and (c) 6 months after the final administration of adjuvant chemotherapy. Total energy expenditure will also be measured by the doubly-labeled water (DLW) method at the first and second time-points. Data will be collected for other factors that may affect weight gain including the particular chemotherapeutic regimen, number of cytotoxic agents in the regimen, route of delivery, menopausal and nodal status, and baseline weight. Patient recruitment was started during this period, and 20 participants have been enrolled to date.